# Does ice do work when it melts or freezes?

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## Main Question or Discussion Point

Since when you freeze liquid water, there's an expansion, wouldn't that mean there's work?

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ProfuselyQuarky
Gold Member
What's the definition of work?

delta W = pAs = pV so a change of volume would indicate a change of work wouldn't it?

Yep ice does work when expanding.
It pushes some atmosphere away...
A thought like that turns up in the definition of enthalpy.

A little disclaimer: The energies in this(only for ice not other enthalpy stuff) are absolutely pathetic.

ProfuselyQuarky
Gold Member
delta W = pAs = pV so a change of volume would indicate a change of work wouldn't it?
Right. In this way, work is dependent on volume. So ice does work when it's expanding. Work is simply the energy required to do something--and the ice is obviously using energy to melt. Actually, it's increasing in energy as it melts.

EDIT: Oh, Tazerfish beat me to it.

I guess what sort of made me wonder about it is when ice melts, the volume doesn't actually change..right? So no work. But if you freeze liquid water, ice expands. So work done?

Ice doesn't change the volume when melting ???
Of course it does.
So the outside does work on the ice.

ProfuselyQuarky
Gold Member
I guess what sort of made me wonder about it is when ice melts, the volume doesn't actually change..right? So no work. But if you freeze liquid water, ice expands. So work done?
Water has a lesser volume than ice.

ProfuselyQuarky
Gold Member

Ooh alright! I was reading a line in my textbook completely wrong. Ah that was dumb Thanks!!

Chestermiller
Mentor
Right. In this way, work is dependent on volume. So ice does work when it's expanding. Work is simply the energy required to do something--and the ice is obviously using energy to melt. Actually, it's increasing in energy as it melts.

EDIT: Oh, Tazerfish beat me to it.
Not only did he beat you to it, but his answer is correct, and yours isn't. Most of the energy involved in melting has nothing to do with the work done by atmospheric pressure. Also, ice receives work from the atmosphere in contracting; it doesn't expand when it melts.

ProfuselyQuarky
Gold Member
Not only did he beat you to it, but his answer is correct, and yours isn't. Most of the energy involved in melting has nothing to do with the work done by atmospheric pressure. Also, ice receives work from the atmosphere in contracting; it doesn't expand when it melts.
I wasn't talking about pressure. I was talking about volume. And I never said ice expands when it melts.

Chestermiller
Mentor
I wasn't talking about pressure. I was talking about volume. And I never said ice expands when it melts.
Work is equal to $\int{P_{ext}}dV$, where, in this case, $P_{ext}$ is atmospheric pressure. So a change in volume in melting ice is accompanied by work being done. This is a small part of the heat of melting.

A little disclaimer: The energies in this(only for ice not other enthalpy stuff) are absolutely pathetic.
It is still able to burst pipes and cause plumbers headaches though